This invention relates to the mounting of sensor devices and, more particularly, to a flexure for holding sensor devices in accurate alignment over a wide temperature range.
Many sensing devices, such as ring laser gyros (RLG's), are sensitive to even very small movements with respect to their supporting structures. This is particularly true when three such devices are grouped together on a common block to measure input rates in three orthogonal directions. Any misalignment from true orthogonality is reflected as device error. In order to maintain accuracy, it is necessary to isolate extraneous movements and correct for them. This is simple for the predictable movement experienced when a support expands and contracts as a unit but not for erratic movements, such as the slipping or "creeping" that occurs when a device is mounted to a support having a different coefficient of thermal expansion and is subjected to changes in temperature. Unlike a simple, unified expansion or contraction, interfacial creeping caused by differences in therefore cannot be rectified.
The problem of interfacial creeping is magnified when the sensing devices are high precision RLG's. In the face of this, exotic materials have been used to eliminate thermal motion by matching the expansion coefficient of the RLG case to that of its support block. A common material for the case of an RLG is Hy-Mu-80, which contains approximately 80% Ni, 5% Mo, 0.5% Mn, 1.5% Si, 0.01% C and the balance Fe. It is preferred for a variety of properties, including the fact that it provides magnetic shielding to the RLG. In order to match the expansion coefficient of Hy-Mu-80, sensor blocks of titanium, beryllium and aluminum matrix material have been proposed. Blocks formed of these materials reduce creeping at the interface with the RLG but have serious disadvantages. Specifically, titanium has a low heat conductivity, beryllium is high in cost and aluminum matrix material is both high in cost and difficult to machine.
Therefore, it is desirable in many applications to provide an inexpensive structure by which sensor devices can be mounted on a common sensor block with no change in input axis alignment over a wide temperature range.